WASHINGTON -- U.S. military officials said Iranian Revolutionary Guard gunships provoked three U.S. naval vessels in the Strait of Hormuz.

Military officials told NBC News Monday that five armed "fast boats" with the Revolutionary Guard Corps approached a Navy frigate and two destroyers in a high-speed formation.

Military accounts of the incident said the Iranian ships broadcast a message saying, "you are going to blow up within minutes."

The U.S. Navy ships went into a defensive posture, sending warning messages to the Iranians to stay clear.

A U.S. official said he believed the Revolutionary Guard was "testing" U.S. defenses.

CNN Monday said the captain of one of U.S. ships was in the process of giving firing orders when the Iranians turned away.

The Revolutionary Guard took over control over naval operations in the Persian Gulf and Strait of Hormuz in summer 2007, prompting concern by U.S. military officials. This was the first provocation since then.